This invention relates to the production of improved aluminum alloy powder-derived products characterized by improved strength properties and therefore useful in structural aerospace components and other applications requiring high strength and relates to methods for producing such improved strength powder-derived products.
The invention here described was made in the course of or under a contract or subcontract thereunder with the United States Air Force.
Aluminum alloys have enjoyed wide use in important applications such as aircraft were aluminum has become well known for its high strength to weight ratio. Various efforts have been employed to further improve the strength of aluminum alloys, including the use of aluminum powder-derived alloy products wherein aluminum powder is compacted and shaped into a useful article. Powder-derived aluminum products are generally considered to have improved mechanical properties such as strength or toughness over many nonpowder-derived products, as shown in various disclosures, for example, U.S. Pat. Nos. 2,963,780, 3,544,392, 3,637,441, 3,899,820, 3,954,458, and 4,104,061, incorporated herein by reference. Nonetheless, there continues a desire to still further improve the strength of powder-derived products.
Powder-derived products are produced from powders made by rapidly quenching atomized liquid aluminum alloys which results in a fine dispersion of intermetallic particles for strengthening compacts formed by squeezing or compacting such aluminum powders. In general, there are two types of aluminum powder alloys, heat treatable and non-heat treatable. In heat treatable alloys fine incoherent intermetallic particles, referred to as dispersoids, serve to control grain size and limit the amount of recrystallization by pinning grain boundaries to result in products with high strength and toughness. On the other hand, non-heat treatable dispersion strengthened aluminum alloys rely on the fine incoherent intermetallics to strengthen the aluminum matrix by impeding dislocation motion (plastic flow) due to their close spacing. In both alloy types it is desirable to maintain the dispersoid and intermetallic particles in a fine size and spacing to achieve good combination of strength and toughness. Various alloy refinements and process refinements have gone forward in order to further the property gain achieved by such dispersion hardening and there is a continuing desire to further improve the strength of compacted aluminum powder products. A strength increase of 5 to 10% is considered highly significant, and an increase of from 10 to 20% is considered extremely desirable, especially where such can be achieved by processing conditions which do not alter the alloy composition so as to permit continued use of known and reliable compositions but at a higher strength level.